An undulator is developed in modern times and has been widely applied to various fields, such as radiation experiment, solid state physics, biology and medical science. Nowadays, other applications for new uses of the undulator is still being researched.
Linear Accelerator is one type of the undulators in early days, in which an electric field occurs through several field generators arranged in line, e.g., electrode collar, so as to accelerate the charged particle continuingly by changing the electric property of the surface of the electric field. However, with the charged particle becomes faster and faster, the field generators must keep high voltage during the acceleration process, it leads not only the high cost but also the risk of safety. In addition, the electric charges exist on the surface of the high-voltage electric field may increase the interference to the charged particle. Further, in terms of the linear accelerators, the length of the path of the charged particle is decided by the length of the field generators, the features results in the linear accelerator with huge size so a waste of space.
Another type of the undulators is Synchrotron, such as a polarizing undulator published by SLAC National Accelerator Laboratory of Stanford University in 2014 (COMMISSIONING OF THE DELTA POLARIZING UNDULATOR AT LCLS, SLAC-PUB-16404), in which the charged particle is acted by a helical magnetic field and an electric field simultaneously so that to move helically in the undulator. Therefore, the path of the charged particle can be extended in the same linear distance.
However, the mentioned helical magnetic field is simulated by four magnetic fields in X-Y plane which are generated by the magnet assemblies set around the charged particle in four directions. Hence, the efficiency of polarization and the magnetic strength are both lower than real helical magnetic field. Moreover, the magnet structure causes the limitation in space to the four magnet assemblies, as a result, the lower uniformity of whole of the magnet field takes a toll on the application of the undulator.